Selective power-down for high performance CPU/system

ABSTRACT

A microelectronic device according to the present invention is made up of two or more functional units, which are all disposed on a single chip, or die. The present invention works on the strategy that all of the functional units on the die are not, and do not need to be operational at a given time in the execution of a computer program that is controlling the microelectronic device. The present invention on a very rapid basis (typically a half clock cycle), therefore, turns on and off the functional units of the microelectronic device in accordance with the requirements of the program being executed. This power down can be achieved by one of three techniques; turning off clock inputs to the functional units, interrupting the supply of power to the functional units, or deactivating input signals to the functional units. The operation of the present invention results in a very significant reduction in power consumption and corresponding heat dissipation by the microelectronic device as compared to the conventional approach of keeping all functional units operational all of the time.

This application is a continuation of application Ser. No. 08/487,976,filed Jun. 7, 1995 U.S. Pat. No. 5,655,124, which is a continuation ofapplication Ser. No. 07/860,717, filed Mar. 31, 1992, U.S. Pat. No.5,452,401.

CROSS-REFERENCE TO RELATED APPLICATIONS

The following are commonly owned, co-pending applications:

"Superscalar RISC Instruction Scheduling" Ser. No. 08/219,425 (AttorneyDocket No. SP035/1397.0170000); and

"Hardware Emulation Accelerator and Method", Ser. No. 08/831,272(Attorney Docket No. SP046/1397.0240000).

The disclosures of the above applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems and methods forreducing power dissipation requirements and power consumed by singlemicroelectronic devices, and more particularly, to dynamic control ofpower consumption by and resultant power dissipation required of suchmicroelectronic devices.

2. Related Art

Power dissipation requirements of microelectronic devices (also calledsemiconductor devices or semiconductor chips or integrated circuits)have become critical in their design, fabrication and use. This isparticularly true with very large scale integrated (VLSI) devices andultra large scale integrated (ULSI) devices, which typically today haveover 1,000,000 transistors (active passive) on a single semiconductordie. The active devices are typically run (clocked) at very high speed(25 MHz and 33 MHz speeds are now typical, with much higher clock ratescontemplated, for example, 250 MHz) in order to achieve desired systemfunctionality and performance.

As is well known, the high clock rate and the high number of activedevices, regardless of the fabrication technology that is used, producesignificant power dissipation requirements when compared to the actualphysical size of the die of the microelectronic device. For purposes ofillustration, a typical die with 1,000,000 active devices is fabricatedon a die 15 mm by 15 mm and requires greater than 132 pinouts. Such amicroelectronic device can operate at a system clock speed of 30 MHzwith 1 micrometer (μm) CMOS technology.

The die must be permanently housed in a suitable housing or package,which among other things (pin out, environmental, physical protection,etc.) must provide adequate heat dissipation in order to prevent failureof the device.

It is not uncommon for a single microelectronic device such as theexample above to generate in the range of 5-10 watts of heat that mustbe dissipated during normal operation. As a result, the junctiontemperature of the die of such a microelectronic device can reach 100°C. for a ceramic package without heatsinking, at the high end of thecommercial temperature range, 70° ambient. The 5-10 watt number willlook small compared to the dissipation requirement for successivegenerations of more powerful microelectronic devices, which areprojected by year 2000 to have 100 million active devices on a singledie. Contemplated die sizes are 25 mm by 25 mm.

Various strategies for packaging have evolved to deal with large heatdissipation. All include some type of heat sink or thermal greasearrangement for rapidly drawing away the unwanted heat so as to protectthe microelectronic device (die and bond wires) from physical failureand performance degradation. Gas, such as air, and even liquid, such aswater, freon, and more efficient coolants are typically used in additionto a conventional heat sink. Heat sink approaches, however, act toincrease physical size, cost, mechanical complexity, and weight of thepackaged microelectronic device. Moreover, the heat dissipation (i.e.,thermal stress) requirements act to limit the physical size of a diethat can be accommodated in a single package.

Representative of the heat dissipation requirements are conventionalmicrocrocessor chips running at clock speeds up to 50 MHz, which cantypically generate 5 watts of dissipated power in normal operation. Inorder to accommodate the heat dissipation requirement, special heatsinks arrangement are provided.

The constant trend in electronics is to reduce the size ofmicroelectronic devices so that smaller and lighter electronic andcomputer products can be made. This miniaturization drive goes onunabated, and historically produces from year to year dramaticreductions in physical size.

The heat dissipation requirement, however, acts as a barrier to thisminiaturization process of electronic and computer devices. In otherwords, the physics of having to dissipate the heat from themicroelectronic device limits the physical size and weight reduction ofthe electronic or computer device that can be achieved. This affects thelifetime of microelectronic devices as well. For example, the reason whya solid state laser has a shorter lifetime than an LED is due toconcentration of heat at a small area.

Another significant ongoing trend in electronics is the increase in thefeatures and functions and the decrease in response time that can beprovided by an electronic or computer device. This is achieved throughmore complex and powerful microelectronic devices. This is the result ofthe increased integration of active devices on a single die. However,additional active devices on the die results in increased heatdissipation requirements, which acts to limit the reduction in the sizeof the microelectronic device package that can be achieved. Even byreducing the power supply voltage, DEC's Alpha CMOS chip, for example,is reported to dissipate 30 watts at 200 Mhz.

The dramatic decrease in the physical size of microelectronic deviceswhen compared to their computational capability, and features andfunctions that they can produce, has resulted in the creation of verysmall personal computers, typically called laptop, notebook and palmtopcomputers. This is the latest benchmark in an ongoing trend to reduce insize computers having powerful features and functions.

A typical portable computer today having a 386SX type microprocessor hasphysical dimensions of 12 in. by 16 in., and a weight of 15 lbs., ofwhich 1 lb. is the rechargeable battery. A typical laptop computer todayhaving a 386SXL type microprocessor has physical dimensions of 8 in. by11 in. by 2 in. and a weight of 5-7 lbs., of which 0.5 lbs. is therechargeable battery.

One of the most critical limiting factors, however, to such notebook(also laptop and palmtop) computers is the battery that is needed to runthe machine. The battery must provide sufficient electrical power sothat the computer can operate for a long enough period of time tosatisfy user demand. Typical operating time for notebook computers todayis in the range of 3 to 4 hours for a single battery charge.

The battery comprises one of the largest components of the computersystem in terms of weight and physical size. However, it is critical forthe user that enough electrical power be provided by the battery so thatdesired computer operation can occur over a sufficient period of time.However, this requirement for operability causes the total size of thecomputer system to increase since the battery physical size must beincreased to meet these requirements.

Consequently, considerable research and development is being directedtowards producing much more efficient batteries for a given size andweight. The goal here is to increase battery technology in chargecapacity so that the resultant battery will provide more power andlonger time for the given size and space. This will in turn act toreduce the size of the computer system that uses it.

In addition to reducing the size of the battery, considerable effort isbeing expended to try to increase the performance of the computer systemin terms of power consumption. One conventional approach as utilized byIntel is to turn off unused peripheral chips. This occurs in the Intel80386 chip set. By turning off unused peripheral chips, significantbattery life can be achieved because the peripheral chips consumedconsiderable amounts of power.

A further approach implemented in AMD's AM386DXL microprocessor chip isto slow down the clock speed (e.g., from 40-0 MHz) to conserve power.

In view of the above, there is a great need for improvement in heatdissipation and power consumption by microelectronic devices,particularly used with computer systems, so as to reduce packagingcomplexity and size and to increase operability time of systems wherebatteries are used to electronically power the microelectronic devices.

SUMMARY OF THE INVENTION

A microelectronic device according to the present invention is made upof two or more functional units, which are all disposed on a singlechip, or die. The present invention works on the strategy that all ofthe functional units on the die are not, and do not need to beoperational at a given time in the execution of a computer program thatis controlling the microelectronic device. The present invention on avery rapid basis (typically a half clock cycle), therefore, turns on andoff the functional units of the microelectronic device in accordancewith the requirements of the program being executed. The operation ofthe present invention results in a very significant reduction in powerconsumption and corresponding heat dissipation by the microelectronicdevice as compared to the conventional approach of keeping allfunctional units operational all of the time.

A representative example of the present invention described herein hasachieved a reduction in power dissipation and power consumption of 30%as compared to the normal conventional approach of keeping all of thefunctional operational units active all of the time during the executionof the computer program. Depending on the architecture of themicroelectronic device and the computer program that is being executed,reductions of 0% to 50% can be achieved. Where single scalar CPU wouldbe on the lower side in comparison to a superscalar CPU architecture,because more blocks may remain idle more frequently.

If the functional units are divided into still smaller blocks, then ahigher percentage of units/blocks can be turned off, given that thenecessary control logic necessary to perform the switching does not addtoo much overhead.

The present invention utilizes several approaches for determining whento turn on and off the functional units of the microelectronic device.One approach utilizes the compiler which compiles the source code of thecomputer program into machine code used to control the operation of themicroelectronic device. A logic unit evaluates (e.g., decodes ormonitors) the machine code during execution, and based on utilizationinformation provided by the compiler, determines at each step in theexecution of the computer program which functional units are needed forexecution, and therefore should be turned on or off. For example, agraphics unit may not need to run when non-graphic operations areexecuting. Similarly, floating point units (FPU) only run 20-30% of thetime in a conventional workstation, thus, it does not need to be onduring idle periods. Cache memory units also lend themselves to controlbased on the present invention.

Another approach used by the present invention for determining when toturn on and off the functional units is that performed using a logicunit on the die that evaluates (monitors) the execution and operation ofthe functional units. This monitoring function produces indications ofupcoming operation (including execution and latency to complete theissued instruction) that can be used for controlling the turn on/turnoff operation of the present invention. In a compact on-chip low costFPU, for example, not all the units can be used at the same time or acollision can result. When an FALU operation is being executed, themultiplier or divider may not be pemitted to run. Power can therefore beshut off to these units.

Any suitable preselected amount of time can be used by the presentinvention for turning on and for tuning off the functional units inaccordance with the requirements of the computer program that is beingexecuted. The turn on/turn off can be as fast as a half-clock cycle, ifdesired, so as to produce maximum power dissipation saving and powerconsumption reduction. Other clock cycle periods for turn on and forturn off can be used. Another method is turning on and off power line(s)to a selected block or blocks.

The present invention contemplates any appropriate electronic approachfor turning on and off a functional unit. In complementary metal oxidesemiconductor (CMOS) circuits, a preferred approach is either (1) tostop the clock signal to the functional unit that is being turned off,or (2) to stop the inputs of the functional unit being turned off fromchanging. Either approach produces the desired result of turning off thefunctional unit The functional unit can be subsequently turned on by theopposite approach that is used for turning it off.

The present invention has particular applicability to CMOS circuitrybecause it takes full advantage of the CMOS characteristic that no poweris consumed by a circuit unless there is a state change. By preventingstate changes in the functional unit(s) not being used at that point inthe execution of the computer program, the present invention can producethe desired power dissipation requirement reduction and powerconsumption reduction. Switching the power buses on/off is notnecessary, and minimal chip area is required for control.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is better understood with reference to thefollowing drawings viewed in connection with the accompanying text.

FIG. 1 is a high level block diagram of a floor plan showingrepresentative functional units of a microelectronic device 100fabricated on a single die 102 in accordance with the present invention.

FIG. 2 is a high level flow chart showing the high level operationalsteps of the present invention.

FIG. 3 is a plot of four traces showing a representative operation of afunctional unit in accordance with the present invention.

FIG. 4 is a block diagram of an embodiment of the present invention forturning on and off the functional units using the system clock signalwith gated control signal.

FIG. 5 is a block diagram of an embodiment of the present invention forturning on and off the functional units by controlling the state of theinputs to the functional units.

FIG. 6 is a block diagram of an embodiment of the present inventionwhere the monitoring information 402 is developed by a compiler inconjunction with compiling each machine code instruction.

FIG. 7 is a block diagram of an embodiment of the present inventionwhere the monitoring information 402 is developed by the instructiondecoding unit and the instruction execution unit operating on themachine code instructions.

FIG. 8 is a block diagram of the embodiment of the present invention ofan optimizing compiler used for reordering the machine code instructionsso as to achieve maximum power saving in accordance with the presentinvention.

FIG. 9 shows a block diagram of a power optimization scheme as appliedto a laptop or palmtop computer in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a system and method for selectively controllingthe power provided to each of the functional units of a microelectronicdevice so that the functional units can be turned on and off as neededby the execution of the computer program that is controlling themicroelectronic device. The dynamic turning on and off of the functionalunits in accordance with the requirements of the program step(s) beingexecuted causes a significant reduction in power (e.g., 10-30%) consumedby the functional units, which results in significant reduction in theheat dissipation requirements and a significant reduction in the powerrequirements of the microelectronic device. The present inventionresults in significant reduction in heat dissipation requirements and inpower requirements for the microelectronic device, which means that heatsink requirements are reduced and battery discharge cycle length isextended, both of which are very desirable results. In addition, powerbus line widths can be reduced. This leads to substantial area savingfor VLSI chips.

FIG. 1 shows the floor plan of a representative microelectronic devicein accordance with the present invention. As shown, the microelectronicdevice represented generally by a reference number 100 has a die 102fabricated, for example, from silicon, having implemented on it thevarious functional units which make up the architecture of theelectronic circuit that is fabricated on die 102. As shown, thesefunctional units in the representative example include: a system clock104, a central processing unit (CPU) 106, a cache control unit (CCU)108, a floating point unit (FPU) 110, a integer unit (INT) 112, and amemory control unit (MCU) 114. It should be understood that thefunctional units that are shown in FIG. 1 are merely for purposes ofillustration. The present invention contemplates any arrangement offunctional units on die 102 of microelectronic device 100. For example,microelectronic device 100 could include memory as well as logicfunctional units. The present invention contemplates present and futurecomputer architectures as implemented on a single semiconductor die orsubstrate.

As shown in FIG. 1, a logic unit 116 is part of microelectronic device100. Logic unit 116, as discussed in greater detail below, operates withsystem clock 104 so as to determine when to turn on and off, and toactually turn on and off the supply of clock signals to the functionalunits in accordance with one embodiment of the present invention.

FIG. 2 shows a high level flow chart which represents the high leveloperation of the system and method of the present invention. Referringnow to FIG. 2, the present invention utilizes four basic operationalsteps.

First, the present invention decodes (or otherwise evaluates) themachine code instructions (compiled from the source code) of thecomputer program that is running on (controlling) microelectronic device100. In this first step, the present invention monitors the machine codeto determine what specific functional unit(s) will be needed to executethe next instruction issued for execution. A preselected clock cycleamount (called CCA only for convenience) before a functional unit(s) isneeded to execute the next machine instruction to be issued, is used asthe time frame that the present invention uses for looking at the nextmachine code instructions before it is issued to be executed. This CCAallows the present invention to take the appropriate logical steps tocause the functional unit(s) to be turned on in time so that the issuedmachine code instruction can be executed in sequence. This first step orblock is indicated by a reference number 202.

In a step or block 204, the present invention removes switch-inhibitingcontrol signals from the functional unit a preselected clock cycleperiod (called clock power up CKPWRUP only for convenience) before thefunctional unit needs to be ready to execute the issued machine codeinstruction. Switching ability is provided during CKPWRUP time frame sothat the functional unit is fully operational when the machine codeinstruction in question is issued to the functional unit. Thus, it canbe seen in this second step that the present invention activates thefunctional unit(s) in question sufficiently prior to when it is neededto execute the machine code instruction so that the functional unit(s)is fully operational when the execution needs to take place.

Any amount of clock cycles can be selected for the CKPWRUP. In apreferred embodiment of the present invention, a single half-clock cycleis used. In other words, the functional unit is activated within asingle half-clock cycle before it is needed for execution of an issuedmachine code instruction. It thus can be appreciated that the functionalunit remains off or in a "stand by" mode (which describes the "no" inputcondition causing no power consumption), until the very last momentbefore it is needed for executing the machine code instruction.

In a third step or block 206, the present invention continues to provideswitching ability to the functional unit for a preselected clock cycleperiod (called clock power on CKPWRON only for convenience). CKPWRON isthe time period (number of clock cycles) required by the functional unitto execute the issued machine code instruction. As such, it includes theclock cycles needed to receive the issued instruction, and the clockcycles equal to the latency period of the functional unit to completethe execution of the instruction.

The fourth and final step or block of the present invention isrepresented by a reference numeral 208. In this fourth step, switchingability is no longer provided to the functional unit after a preselectedclock cycle period (called clock power down CKPWRDN) after thefunctional unit has completed the required task of executing the machinecode instruction of the computer program. In other words, the functionalunit is turned off (de-activated) after it has executed the requiredtask. In this way, the functional unit is not kept on or active after itis no longer needed. A typical value for CKPWRDN is a single half-clockcycle. This activate/de-activate embodiment is appropriate forfunctional units requiring memory, state saving, or the like. Othertechniques are well within the scope of the present invention.

Coupling/decoupling of a power supply bus is also envisioned. Theaddition of a power switch(es) connected between V_(DD) and eachfunctional unit, can be used to turn on and off the supply of power tothe functional units by controlling the power switch (e.g., FET) usingthe above CKPWRON control signal, or the like. In this power-down case,some DC power will be consumed through the power switch, but with thefunctional unit(s) disconnected, overall conservation will result.

The net result of these four steps of the present invention is asignificant reduction in the power consumed by microelectronic device100. This reduction is due to the fact that the functional units are notkept on when they are not needed. As will be explained in detail below,since CMOS technology is used, power is only consumed when a functionalunit is changing state (i.e., switching). Since a functional unit is"off" when it is prevented from changing state, negligible power isconsumed by that functional unit. This means that a functional unit thatis off does not consume power, which results in the power consumptionreduction.

Since power consumption is reduced, the heat dissipation requirements ofdie 102 and associated packaging (not shown) of microelectronic device100 is reduced. In addition, when a battery source is used, it can bemade smaller for a given operational period of time. Furthermore,because power consumption is reduced, the line width of power supplybuses can also be reduced.

A representative example of the operation of the present invention inaccordance with the flow chart of FIG. 2 is now described with referenceto FIG. 3. FIG. 3 shows four traces, each having the same timeframe onthe horizontal axis. The vertical axis of each trace indicates theamplitude of a signal or the state of a functional unit, or the state ofoperation in accordance with the present invention, as described below.Upper trace 301 shows waveform 302 which is the output of system clock104 (FIG. 1) that is the clock for all of the functional units whichmake up microelectronic device 100. The two system clocks are 180° outof phase from one another.

The representative functional unit for FIG. 3 that is chosen for thisexplanation is floating point unit (FPU) 110. As is discussed below inthe example section, it turns out that FPU 110 in many computer systemsis used about 10% of the time. Consequently, the present inventionproduces significant reduction in power dissipation requirements andpower consumption as it relates to FPU 110, as will become moreapparent.

Third trace 305 shows the execution of two floating point operations.The first floating point operation, labeled A, is indicated by a box306. Box 306 represents the number of clock cycles required to performfloating point operation A. Similarly, floating point operation B asindicated by a box 318 is also illustrated and shows the number of clockcycles that are required to execute it. Specifically, 51/2 clock cyclesare required to perform the floating point operation A, and two clockcycles are required to perform the floating point operation B. It shouldbe understood that these timeframes are merely for purposes ofillustration. In fact, it may be in actual practice that the floatingpoint operation will require scores of cycles to be performed. Inaddition, there may be thousands of cycles between each floating pointoperation. However, FIG. 3 is not large enough to represent thisgraphically. Thus, the spacing between the floating point operations Aand B and the length of each have been made arbitrarily small forpurposes of illustration.

Fourth trace 307 of FIG. 3 illustrates the four steps that take placewith respect to each of the floating point operations A and B. Withrespect to floating point operation A, the CCA period is represented asrequiring three half-cycles. This CCA period is indicated by referencenumeral 308. A CKPWRUP period for floating point operation A is singlehalf-clock cycle, and is indicated by a time block 310. The amount oftime that floating point operation A takes corresponds to the CKPWRONperiod represented by a time block 312. Finally, a CKPWRDN period is ahalf-clock cycle, and is represented by a time block 314.

The actual operation of FPU 110 to execute floating point operation A iscontrolled in accordance with the present invention by providing systemclock 302 to the clock input of FPU 110 for the time period of the clockcycles indicated by reference numeral 304 of trace 303. It is seen intrace 303 that the system clock provided at the FPU clock input isprovided one-half clock cycle before the beginning of the execution offloating point operation A, and is left on for one-half clock cycleafter the completion of floating point operation A.

A similar example is shown for floating point operation B. Referringagain to trace 307, the CCA period is indicated by a time block 320,which for purposes of illustration is shown as requiring threehalf-cycles. A CKPWRUP time block 322 is one-half clock cycle. A CKPWRONtime block 324 is two clock cycles, which corresponds to the time framerequired by FPU 110 to complete the floating point operation B. Finally,a CKPWRDN time block 326 is a one-half clock cycle.

FIG. 3 illustrates the power saving that results in accordance with theoperation of the present invention. Specifically, with reference totrace 303, it can be seen that the state of FPU 110 is allowed to changeonly when there is a clock signal applied to the FPU clock input. Inother words, FPU 110 in the illustrated example is only operationalduring period 304 and during period 316, and is not operational duringthe intervening time periods. Thus, it can be seen where the powersavings occur in accordance with the present invention.

It should be appreciated that all of the functional units in themicroelectronic device 100 are being similarly controlled by the presentinvention so that only the functional unit(s) that is needed to executethe latest machine code instruction being issued is powered on. Allother unneeded functional units are powered off. Thus, significant powersavings result in accordance with the present invention.

The present invention has particular applicability to CMOS integratedcircuitry. The reason for this is that CMOS circuits only consume powerwhen they change state. In other words, power is only consumed whenswitching is occurring. Viewed from the transient or alternating current(AC) domain, the amount of power consumed to switch a node isproportional to CV², where C=the capacitance in farads for the switchednode, and V is the voltage from rail V_(SS) to rail V_(DD). From thesteady state or direct current (DC) perspective, the amount of powerconsumed is equal to 5-15%, depending on manufacturing process valiablesand input slew rate.

CMOS should be compared to BiCMOS, where the power consumption of thebipolar circuit can not be turned off, due to "low" input resistancethrough the base of the device and current control mechanisms used. Incontrast, CMOS (and MOS devices in general) have a high input impedanceat the gate electrode due to the gate oxide's electrical isolationproperties.

CMOS should also be compared to bipolar transistor circuitry as well.Bipolar transistors consume electrical power regardless of whether anyswitching is occurring. In other words, current is flowing in thecircuit even when no switching is taking place. This is the reason whyCMOS technology has become the technology of choice in integratedcircuits, due to its low power consumption, scaling-down of powersupplies (e.g., batteries for portable computers) is feasible.

The present invention is particularly applicable for CMOS circuitry. Itis also applicable for BiCMOS, NMOS, MESFET, I² L and GaAs circuitry aswell.

The present invention contemplates any suitable approach for controllingwhether the state of a functional unit is allowed to change. Thiscontrol of state changes turns the functional unit on and off, andproduces the desired power reduction in accordance with the presentinvention.

Referring now to FIG. 4, one representative approach for controlling thestate of a functional unit in accordance with the present invention isshown. This approach controls providing system clock signal 302 to thefunctional unit in question. The functional unit only consumes powerwhen the present invention provides system clock signal 302. Referringnow to FIG. 4, logical unit 116 of the present invention evaluates (bydecoding for example) issuance of machine code instructions via a path402 in accordance with any suitable approach, discussed below.Intelligence provided by path 402 allows logic unit 116 to know when toturn on and off various functional units in accordance with the presentinvention.

System clock 104 provides system clock signal 302 to logic unit 116. Forpurposes of illustration, four functional units are shown, labeled #1,#2, #3, and #4. Reference numeral 406 corresponds to functional unit 1,reference numeral 410 corresponds to functional unit 2, referencenumeral 414 corresponds to functional unit 3, and reference numeral 418corresponds to functional unit 4. Each functional unit 406, 410, 414 and418 has a corresponding clock input line 404, 408, 412, and 416,respectively.

In operation, logic unit 116 provides system clock signal 302 on theappropriate clock input line for the functional unit that is beingturned on. When that functional unit is to be turned off, logical unit116 no longer provides system clock 302. Since the functional unitcannot change state without provision of the clock signal, no power isconsumed by functional units not receiving clock signal 302. This is howa functional unit is turned on or off by turning clock signal 302 on oroff.

An alternate approach for turning on and off the functional units isshown in FIG. 5. Referring now to FIG. 5, this embodiment turns on andoff functional units 406, 410, 414, and 418 by controlling the statechange of the inputs for these functional units. By not allowing theinputs of functional units that are off to change state, this approacheffectively turns off such functional units. Only the inputs offunctional units that are on are allowed to change state.

FIG. 5 shows one embodiment for accomplishing this strategy. Onetechnique to keep the inputs from switching is to latch and hold theprevious input (shown at 502) using a known gated latch device (seelatches 504, 510, 516 and 522, for example). Latches 504, 510, 516 and522 are controlled to pass the latched inputs via control lines 508,514, 520 and 526, which can be generated by logic unit 116 based onsignal 402, as will become evident to those skilled in the art.Alternatively, the inputs can be forced to a high impedance value bylogically ANDing the input with a control signal. Many otherfunctionally equivalent techniques will become readily apparent to thoseof ordinary skill in the art.

Similar structure and operation applies to functional unit 410,functional unit 414, and functional unit 418. Therefore, separatediscussion of them is not required.

The present invention contemplates other approaches for turning on andoff functional units by the logic unit 116. The embodiments of FIGS. 4and 5 are merely for purposes of illustration.

The present invention can utilize several approaches for obtaining themonitoring information on line 402 used by logic unit 116 to determinewhen to turn on and off each of the functional units during theexecution of the machine code instructions.

A representative approach is shown in FIG. 6. A computer program insource code form, designated by a reference numeral 602, is supplied toa compiler 604 for compiling source code 602 into machine code. Compiler604 produces machine code instructions after compiling the source code.For purposes of illustration, six machine code instructions 606, 610,614, 618, 622, and 626 are shown. Each machine code instruction has acorresponding functional unit data block, which comprises the monitoringinformation that is supplied by path 402 to logic unit 116. Thefunctional unit data accompanying a given machine code instruction thuscan allow logic unit 116 to operate microelectronic device 100 inaccordance with the present invention.

An alternate embodiment for providing monitoring information on line 402is shown in FIG. 7. Here, the actual operation of a reduced instructionset computer (RISC) superscalar microprocessor, which is a typicalapplication for the present invention, provides the monitoringinformation on line 402 as follows. Source code computer program 602 issupplied to a compiler 702, which produces machine code instructions704. The machine code instructions are supplied first to an instructiondecoding unit (IDU) 706. The decoded instructions from IDU 706 aresupplied to an instruction execution unit (IEU) 708.

IDU 706 and IEU 708 in performing the out-of-order execution providesthe decoded information 402 as indicated. This decoded information maytake the form of data dependency information, instruction issuinginformation, or the like. The information is available from instructionscheduling logic. An example of instruction scheduling logic is found incommonly owned copending application titled, "Superscalar RISCInstruction Scheduling" Ser. No. 08/219,425 (Attorney Docket No.SP035/1397.0170000).

FIG. 8 shows an embodiment of the present invention using an optimizingcompiler 802 to order the machine code instructions in a way whichmaximizes the power saving produced by the present invention. This powersaving is achieved by reordering the machine code instructions from theorder derived from the source code. The reordering is done so as tooptimize the reduction in power consumption by microelectronic device100 in connection with running computer program 602.

A representative block diagram showing such an optimization is in FIG.8. As shown, optimizing compiler 802 produces output in the form ofreordered machine code instructions. For purposes of illustration, thesame machine code instructions with accompanying functional unit datafound in FIG. 6 are used to show the reordering concept. It is seen thatthe machine code instructions with their associated FUD are reordered.This example is to illustrate that reordering can produce optimizationin terms of power consumption reduction.

The reordered machine code instructions are then issued to thefunctional units, which are controlled by logic unit 116 in accordancewith the operation described in connection with FIG. 6. When compiler802 determines that one or more functional blocks are not used afterinstruction 1 for some number of cycles, it can send disable or powerdown signals to those one or more functional blocks in order to stopclocking, block inputs or shut off the power supply, as the case may be,until the one or more blocks are need in the future.

For a 5W chip, Table 1 shows representative percentage of use and powersavings. Note that the total power down savings represents 46% (2.3/5).

                  TABLE 1                                                         ______________________________________                                        Functional Wattage    Percentage of                                                                             Power Down                                  Unit       Requirement                                                                              Use         Savings                                     ______________________________________                                        Floating Point                                                                           1.5        10          1.35                                        Integer    1.0        90          0.10                                        Memory     2.0        75          0.50                                        Graphics   0.5        30          0.35                                        TOTAL SAVINGS                 2.30W                                           ______________________________________                                    

The "selective power down" techniques of the present invention mayeasily be applied to the highly structured functional units/modulesdisclosed in a commonly owned, co-pending application titled "HardwareEmulation Accelerator and Method", Ser. No. 07/831,272 (Attorney DocketNo. SP046/1397.0240000), the disclosure of which is incorporated hereinby reference.

Laptop Notebook and Palmtop Computer Optimization Strategy

As discussed above, the present invention produces significant savingsin power consumption. This has very direct impact on laptop and palmtopcomputers, where weight is a very critical, if not the most critical,factor in terms of user acceptance. Even a reduction in 0.25 kg can beenough for a user to select that particular computer over a heavierversion. Even though significant strides have been made in terms ofbattery technology resulting in significant weight reduction, anyreduction in power consumption would be extremely important since itwould produce much longer life of operation for a given battery andbattery charge.

FIG. 9 shows a block diagram of one strategy that can be used inaccordance with the present invention. As shown, the user can select alonger battery life option when operating the laptop or palmtopcomputer. This is indicated by 1002. Once this option is selected, thepresent invention utilizes an optimization scheme, as indicated byreference numeral 904, which acts to minimize the power consumption ofthe microelectronic device. This could come in many different forms suchas reordering of machine code instructions or operating particularfunctional units separate and apart from each other.

This approach has particular applicability to situations where thelaptop or palmtop computer is being used for an extended period of timeaway from a standard voltage source. In other words, the unit is beingrun entirely by battery. The user desires to maximize the operationaltime of the laptop or palmtop computer in such situation. Thisoptimization approach allows this to be achieved.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. Thus the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A system for controlling the supplying of asystem clock signal to each of at least two functional units of amicroelectronic device, said system comprising:(a) a compiler forcompiling a stream of source code instructions into a stream of machinecode instructions; (b) an instruction decoding unit for decoding saidstream of machine code instructions and for examining a machine codeinstruction within said stream of machine code instructions a firstpreselected number of system clock cycles before execution of saidmachine code instruction to determine which of the at least twofunctional units will execute said machine code instruction; (c) aninstruction execution unit for causing said stream of machine codeinstructions to be executed by the at least two functional units and fordetermining when execution of said machine code instruction within saidstream of machine code instructions is complete; (d) first logic means,coupled to said instruction decoding unit, for causing the system clocksignal to be supplied to the functional unit needed to execute saidmachine code instruction a second preselected number of system clockcycles before said machine code instruction is executed; and (e) secondlogic means, coupled to said instruction execution unit and to saidfirst logic means, for causing the system clock signal to be supplied tothe functional unit executing said machine code instruction until theexecution of said machine code instruction is complete as determined bysaid instruction execution unit, whereby the power consumption of saidmicroelectronic device is reduced.
 2. The system of claim 1, whereinsaid instruction execution unit is configured to execute RISCinstructions in an out-of-order manner, wherein said RISC instructionsare scheduled in order to reduce power consumption and heat dissipationrequirements of said microelectronic device.
 3. The system of claim 1,wherein said first and second logic means cause the system clock signalto be supplied continuously to the functional unit executing saidmachine code instruction so long as said first logic means determinesthat each successive machine code instruction in said stream of machinecode instructions will be executed on the same functional unit.
 4. Asystem for reducing power consumption and heat dissipation requirementsin a microelectronic device, said microelectronic device having at leasttwo functional units switchingly coupled to a power supply, said systemcomprising:(a) a compiler for compiling a stream of source codeinstructions into a stream of machine code instructions; (b) aninstruction decoding unit for decoding said stream of machine codeinstructions and for examining a machine code instruction within saidstream of machine code instructions a first preselected number of systemclock cycles before execution of said machine code instruction todetermine which of the at least two functional units will execute saidmachine code instruction; (c) an instruction execution unit for causingsaid stream of machine code instructions to be executed by the at leasttwo functional units and for determining when execution of said machinecode instruction within said stream of machine code instructions iscomplete; (d) one or more power switches coupled to said instructiondecoding unit, said instruction execution unit, the power supply and theat least two functional units; (e) first logic means, coupled to saidinstruction decoding unit and said one or more power switches, forcontrolling the supplying of power from the power supply to thefunctional unit needed to execute said machine code instruction so thatpower is supplied a second preselected number of system clock cyclesbefore said machine code instruction is executed; and (f) second logicmeans, coupled to said instruction execution unit, said first logicmeans, and said one or more power switches, for controlling thesupplying of power from the power supply to the functional unitexecuting said machine code instruction so that power is supplied untilthe execution of said machine code instruction is complete as determinedby said instruction execution unit, whereby the power consumption ofsaid microelectronic device is reduced.
 5. The system of claim 4,wherein said instruction execution unit is configured to execute RISCinstructions in an out-of-order manner, wherein said RISC instructionsare scheduled in order to reduce power consumption and heat dissipationrequirements of said microelectronic device.
 6. The system of claim 4,wherein said first and second logic means cause power to be suppliedcontinuously to the functional unit executing said machine codeinstruction so long as said first logic means determines that eachsuccessive machine code instruction in said stream of machine codeinstructions will be executed on the same functional unit.
 7. A systemfor a microelectronic device for reducing power consumption and heatdissipation requirements, said microelectronic device having at leasttwo functional units, the at least two functional units receivingrespective input signals, said system comprising:(a) a compiler forcompiling a stream of source code instructions into a stream of machinecode instructions; (b) an instruction decoding unit for decoding saidstream of machine code instructions and for examining a machine codeinstruction within said stream of machine code instructions a firstpreselected number of system clock cycles before execution of saidmachine code instruction to determine which of the at least twofunctional units will execute said machine code instruction; (c) aninstruction execution unit for causing said stream of machine codeinstructions to be executed by the at least two functional units and fordetermining when execution of said machine code instruction within saidstream of machine code instructions is complete; (d) one or more inputswitches coupled to said instruction decoding unit, said instructionexecution unit, the respective input signals and the at least twofunctional units; (e) first logic means, coupled to said instructiondecoding unit and said one or more input switches, for controlling theactivation/deactivation of the respective input signals to thefunctional unit needed to execute said machine code instruction so thatsaid functional unit is activated a second preselected number of systemclock cycles before said machine code instruction is executed; and (f)second logic means, coupled to said instruction execution unit, saidfirst logic means, and said one or more input switches, for controllingthe activation/deactivation of the respective input signals to saidfunctional unit so that said functional unit is activated until theexecution of said machine code instruction is complete as determined bysaid instruction execution unit, whereby the power consumption of saidmicroelectronic device is reduced.
 8. The system of claim 7, whereinsaid instruction execution unit is configured to execute RISCinstructions in an out-of-order manner, wherein said RISC instructionsare scheduled in order to reduce power consumption and heat dissipationrequirements of said microelectronic device.
 9. The system of claim 7,wherein said first and second logic means cause the functional unitexecuting said machine code instruction to be continuously activated solong as said first logic means determines that each successive machinecode instruction in said stream of machine code instructions will beexecuted on the same functional unit.
 10. A system for prolonging thelife of a battery operating within a laptop computer system, said laptopcomputer system having at least two functional units controlled by aclock signal produced by a clock unit, the system comprising:(a)interface means for allowing a user to select a battery power savingmode of operation; and (b) power reduction means, responsive to saidinterface means, for reducing power consumption of the laptop computer,including:(1) an instruction decoding unit for decoding a stream ofmachine code instructions and for examining a machine code instructionwithin said stream of machine code instructions a first preselectednumber of system clock cycles before execution of said machine codeinstruction to determine which of the at least two functional units willexecute said machine code instruction, (2) an instruction execution unitfor causing said stream of machine code instructions to be executed bythe at least two functional units and for determining when execution ofsaid machine code instruction within said stream of machine codeinstructions is complete, (3) first logic means, coupled to saidinstruction decoding unit, for causing the system clock signal to besupplied to the functional unit needed to execute said machine codeinstruction a second preselected number of system clock cycles beforesaid machine code instruction is executed, and (4) second logic means,coupled to said instruction execution unit and to said first logicmeans, for causing the system clock signal to be supplied to thefunctional unit executing said machine code instruction until theexecution of said machine code instruction is complete as determined bysaid instruction execution unit, whereby the power consumption of saidmicroelectronic device is reduced; whereby the power consumption of saidlaptop computer system is reduced by controlling the supplying of theclock signal to the at least two functional units.
 11. The system ofclaim 10, wherein said instruction execution unit is configured toexecute RISC instructions in an out-of-order manner, wherein said RISCinstructions are scheduled in order to reduce power consumption and heatdissipation requirements of said microelectronic device.
 12. The systemof claim 10, wherein said first and second logic means cause the systemclock signal to be supplied continuously to the functional unitexecuting said machine code instruction so long as said first logicmeans determines that each successive machine code instruction in saidstream of machine code instructions will be executed on the samefunctional unit.